It will take even tougher talks if the much-criticized and fragile first agreement is to become a long-term deal that will come closer to mollifying all sides.

GENEVA — Turning the fragile preliminary agreement on Iran's nuclear program into a stringent long-term deal will require even harder negotiations than those in the arduous months leading up to Sunday's signing ceremony in Geneva.

New issues will be added to the complex mix even while the two sides try to maintain enough momentum to avoid having their temporary deal settle into a slightly altered status quo that satisfies no one. And the talks will take place amid fierce crossfire from critics on both sides.

The criticism became apparent within hours of the deal as Israeli Prime Minister Benjamin Netanyahu attacked it as a"historic mistake" that makes the world a "much more dangerous place."

The Obama administration and its partners from Britain, France, Germany, Russia and China had agreed to weaken international sanctions against Iran in return for "cosmetic Iranian concessions that can be canceled in weeks," Netanyahu charged.

The preliminary deal requires a pause in Iran's effort to build its nuclear capacity by enriching uranium. It rolls back some elements of that country's nuclear program and subjects it to daily international inspections. But the pause comes at a point where analysts believe Iran already has gotten within a few months of having enough enriched uranium to test a nuclear device, should it decide to do so.

The prospect of Iran being that close to acquiring bomb-making capability deeply disturbs Israel, as well as Saudi Arabia and other Arab states in the Persian Gulf.

Because of the deep suspicion of Iran's motives on the part of long-standing allies, U.S. officials have emphasized that the current agreement is just a means to a deal that would permanently move Iran away from the ability to make a nuclear weapon.

"You can't get everything in the first step. You have to go down the process here," Secretary of State John F. Kerry said on CBS' "Face the Nation."

"What we've done is lock components of their program in place and actually roll some of them backwards," Kerry said. "We believe it now opens the door to our going into the larger, more comprehensive arrangement by which Iran will have to prove that its program is really peaceful."

President Obama called Netanyahu on Sunday to discuss the deal. The White House said Obama told Netanyahu that he wanted the two countries to begin consultations on the next round of negotiations and that Israel "has good reason to be skeptical about Iran's intentions."

The administration and its allies hope that the agreement will gradually gain support and build momentum. Lifting some sanctions on Iran's economy will build a constituency within Iran for more relief, they hope. At the same time, stringent inspections of Iran's nuclear sites could build support in the U.S. and elsewhere for further negotiations.

But the opposite could also happen. If the talks bog down, momentum could slow and the administration could end up simply extending the current arrangement so that it becomes a long-term status quo.

That would not satisfy either side.

Settling for the interim agreement over the long term would leave the effort to curb Iran's nuclear program in an uncomfortable limbo, neither permitting a breakout, as happened with North Korea in 2006, nor achieving a total rollback of the nuclear program, as happened in Libya in 2003.

Enshrining the current agreement as the long-term future could be "practically the worst of all possible outcomes," former CIA Director Gen. Michael Hayden said on CNN.

That outcome would leave Iran too close to a nuclear "breakout," he said. At the same time, the administration would face mounting trouble in holding together the international coalition that has enforced economic sanctions against Iran.

The Geneva agreement calls for negotiating a final deal within one year and says the preliminary six-month deal can be renewed by mutual consent. Many analysts believe that extending the existing deal at least once is likely because of the complexity of the negotiations. Administration officials insist, however, that they won't renew it indefinitely and are ready to call a halt if they do not make headway.

Cliff Kupchan, an Iran specialist and former State Department official, said he believes a final deal can probably be worked out because of Iran's desperate need for economic relief and Americans' recognition that the deal's terms are favorable for them.

Yet the challenges are so great that whether a deal falls into place "is going to be a close call," said Kupchan, now with the Eurasia Group risk assessment firm.

To clinch the final deal, the U.S. and its allies will have to persuade Iran to agree to far-reaching dismantling of much of a nuclear infrastructure that has cost billions of dollars and become a symbol of national pride.

The current agreement imposes tough new monitoring requirements, including daily visits by inspectors to enrichment facilities; but the comprehensive deal would be even more intrusive.